work and strategy for gathering information necessary fof watershed delineation and protection. Cape Cod is a 260-hectare peninsula formed by retreating ice sheets during the Pleistocene epoch. Thus, the Cape is largely composed of sand and till materials. The characteristics of these materials and the origins of their placement have created a hydrologic system dominated by groundwater. On Cape Cod. the delineation of watersheds is characterized by the configuration of the
(MaBsachusettsl Commission flrovides insights into how watershed flroteaion might work nationwide.
groundwater "lenses" (groundwater flvw in unconsolidated aquifer systems usually has a lens shape; set: Figure 1 ) rather than by topographic configurations (Figure 2). The "groundwater divide" is a watershed boundary at which a drop of precipitation falling on one side will flow to one resource and a drop on the other side will flow ta another resource. The groundwater Lenses are in a state of dynamic equilibrium with the surrounding saline w a t a s ; precipitation recharges the aquifer as the lenses dis-
Environ. SCI.Technol., Vol.'ZJ
No 9. 1993 1737
charge along the coasts. Groundwater is the primary drinking-water supply for the Cape: it discharges into ponds and coastal embayments and is the primary disposal area for wastewater from the population of the Cape. The RF’P addresses the conflicting needs of water quality preservation and wastewater disposal by identifying the water resourcas of concern, establishing watershed-specific standards that development proposals must meet, and establishing a framework for obtaining the information required to protect the resources and equitably allow development in the watersheds. Through the RFT, the Commission has targeted nitrogen as the conservative groundwater contaminant on which land use intensity in watersheds will be limited. Nitrogen was chosen primarily because it is usually the limiting nutrient in saline waters and has an established EPA drinking water standard; thus it is useful in addressing watershed or recharge amas for both fresh and salt water ecosystems. Nitrogen generally is regarded as not being attenuated once it reaches the groundwater because once there-usually in the form of nitratwoncentrations generally don’t decrease, probably because of its negative c h q e and oxygenated conditions in the aquifer. “Limiting nutrient” is the chemical 1738 Envimn. Sci. Technol.. Vol. 27, No. 9, 1993
constituent that is the least abundant but necessary for growth in these systems. Because it is necessary, its paucity limits the growth of algae and everything else in the food chain.
The method of the Commlsslon has heavily on a nix of sclence and land use Classification scheme The RPP divides groundwater on the Cape into six classifications (Figure 3). The Commission has established a nitrogen-loading methodology with a standard of 5 ppm for watersheds that supply drinking water wells (these watersheds are also known as wellhead protection areas or zones of contribution). Coastal water standards are based on the individual surface water flushing characteristics of each embayment (or small bay, which may have a river flowing into it]. In areas where documentation has been pro-
vided showing that water quality is already above the coastal watershed standard, the RPP requires that development proposals show how water quality can be improved or show that the development will not cause a net addition of nitrogen. This method of watershed protection depends heavily on having documented land use and geographic information technology to detail the amount of nitrogen loading. Once watersheds are established, an assessment of nitrogen loading from all land uses (point and nonpoint] is conducted based on the available land use details. An analysis of potential land use of undeveloped land in the watershed establishes the upper bound of the impact of land use on water quality. If the analysis of potential land use, or “build-out,’’indicates that future development will surpass the standard for the watershed, restrictions-including increased minimum lot size and purchase of developable land for dedicated open space-are recommended. The methodology and strategy adopted by the Commission have revealed operational difficulties and information needs. Funds for flushing studies to establish the amount of nitrogen loading that coastal waters can assimilate are difficult to obtain. Flushing studies have found that stricter nitrogen
r loading controls are needed in portions of the watershed (“subwatersheds”] that drain to smaller, slower flushing portions of the main coastal embayments, referred to as “subembayments.” Watersheds that supply drinking water wells can be similarly divided on the basis of “time of travel” zones, modeled areas based on the amount of time a certain amount of water will take to reach a supply well with a given pumping rate. Watershed delineations cannot be finalized until refined regional water table maps are prepared, although less refined maps can provide an
adequate approximation. Finally, land use controls based on criteria other than water quality as measured by the level of a single contaminant must be adopted to prevent undesirably intense land use. This is becoming more pertinent on Cape Cod as technology is introduced that reduces the amount of nitrogen applied to our watersheds. Science and land use planning The method of regulation that the Commission has adopted depends heavily on a mix of science and land use planning. In other areas of the country, the information base avail-
able on Cape Cod may not exist, and the idea of land use planning may be antithetical to local concerns. More complex hydrologic systems Eduord M. Eichner is on environmental scientist for the Cope Cod Commission in Bornstable, MA. His degrees include o B.S.in b i d oev from the Uni&;ty of Oregon, on M.S. in ennmnmental science and a Master of Public Affoirsfrom Indiana University. Environ. Sci. Technol., Vol. 27, No. 9, 1993 1739
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Through all discussions of watei shed protection and managemen we must remain focused on the spc cific water resource to he protecte and on the cumulative effect that a land uses-from l a r g e industri: water users to single f a m i l y res dences-have on water quality.
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